<template>
  <div class="pagination">
    <button :disabled="pageNo === 1" @click="nowPage -= 1">上一页</button>
    <button
      v-show="startEnd.start > 1"
      @click="nowPage = 1"
      :class="nowPage === 1 ? 'active' : ''"
    >
      1
    </button>

    <button v-show="startEnd.start > 2">···</button>

    <!-- 
      避免v-if和v-for的一起使用
     -->
    <button
      v-for="item in pageContainer"
      :key="item"
      @click="nowPage = item"
      :class="nowPage === item ? 'active' : ''"
    >
      {{ item }}
    </button>

    <button v-show="startEnd.end < totalPages - 1">···</button>
    <button
      v-show="startEnd.end < totalPages"
      @click="nowPage = totalPages"
      :class="nowPage === totalPages ? 'active' : ''"
    >
      {{ totalPages }}
    </button>
    <button :disabled="pageNo === totalPages" @click="nowPage += 1">
      下一页
    </button>

    <button style="margin-left: 30px">共 60 条</button>
  </div>
</template>

<script>
export default {
  name: "Pagination",
  props: ["totalPages", "pageNo", "continueNum"],
  data() {
    return {
      nowPage: this.pageNo,
    };
  },
  computed: {
    startEnd() {
      let start = 1;
      let end = 1;
      //首先判断总页数是否小于连续页长度,连续页的开始就是1 结束就是连续页的长度
      if (this.totalPages < this.continueNum) {
        start = 1;
        end = this.totalPages;
      } else {
        //连续页长度小于总长度
        // 根据当前页和连续页长度 计算出连续页开头 和 连续页结尾 的值
        start = this.pageNo - Math.floor(this.continueNum / 2);
        end = this.pageNo + Math.floor(this.continueNum / 2);

        //还要判断,因为start可能小于1,让start等于1 end等于连续页
        if (start < 1) {
          start = 1;
          end = this.continueNum;
        }

        //还要判断,因为end的值可能大于totalPages,让end变成总页数,计算start
        if (end > this.totalPages) {
          end = this.totalPages;
          start = this.totalPages - this.continueNum + 1;
        }
      }

      return {
        start,
        end,
      };
    },
    pageContainer() {
      const { start, end } = this.startEnd;
      const arr = [];
      for (var i = start; i <= end; i++) {
        arr.push(i);
      }
      return arr;
    },
  },
  watch: {
    nowPage() {
      this.$emit("changePageNo", this.nowPage);
    },
  },
};
</script>

<style lang="less" scoped>
.pagination {
  button {
    margin: 0 5px;
    background-color: #f4f4f5;
    color: #606266;
    outline: none;
    border-radius: 2px;
    padding: 0 4px;
    vertical-align: top;
    display: inline-block;
    font-size: 13px;
    min-width: 35.5px;
    height: 28px;
    line-height: 28px;
    cursor: pointer;
    box-sizing: border-box;
    text-align: center;
    border: 0;

    &[disabled] {
      color: #c0c4cc;
      cursor: not-allowed;
    }

    &.active {
      cursor: not-allowed;
      background-color: #409eff;
      color: #fff;
    }
  }
}
</style>
